Researchers at Waikato Hospital (Hamilton, New Zealand) conducted a prospective study involving a cohort of 112 patients admitted with community-acquired pneumonia during winter. The researchers looked for associations between mortality and serum levels of 25-hydroxyvitamin D, cathelicidin, and β-defensin-2, based on the hypothesis that vitamin D deficiency would be associated with lower levels of the other two antimicrobial peptides, whose synthesis is known to be regulated by vitamin D.
The results showed that severe 25-hydroxyvitamin D deficiency (less than 30 nmol/L) was common in this population (15%) and was associated with a higher 30-day mortality compared with patients with sufficient 25-hydroxyvitamin D (over 50 nmol/L). These associations were not explained by differences in age, comorbidities, or the severity of the acute illness. Neither cathelicidin nor β-defensin-2 levels predicted mortality, although there was a trend towards increased mortality with lower cathelicidin; neither cathelicidin nor β-defensin-2 levels correlated with 25-hydroxyvitamin D. The study was published in the May 2011 issue of Respirology.
"These observations raise the possibility that vitamin D supplements and cathelicidin could have a therapeutic role in acute infections,” concluded lead author Leong Leow, MD, and colleagues of the respiratory research unit.
The authors point out several study limitations; first, an observational study cannot demonstrate a causal relationship between 25-hydroxyvitamin D levels and mortality, and it is possible that the 25-hydroxyvitamin D blood level is a biomarker for frailty and poor prognosis. Second, the findings cannot be generalized to nonhospitalized patients with pneumonia who are treated in the community. The researchers also speculated that given that the main source of vitamin D for most people is sunlight exposure, deprivation of sunlight during the winter months might plausibly contribute to the increased prevalence of pneumonia during this time.
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